The present invention relates to a filter cartridge made of an accordion fold pack folded in a zigzag shape which can be used in a frame in ventilating systems, air-conditioning systems and the like. The design of the accordion fold pack and the choice of the material used for it depends on the filter""s technical properties and the required air throughput.
From German Patent 195 12 678 C1, for example, a filter cartridge is known. The filter cartridge in that patent is designed as an accordion fold pack and made of a thermoplastic heat sealable nonwoven fabric. A recurring problem with such filters is sealing it at the frame or housing in which it is set. To solve this problem, the known filter cartridge offers a combined sealing and stiffening bracket, covering the end face of the accordion fold pack. The sealing and stiffening bracket in cross-section, is shaped like a radical (i.e. {square root over ( )}). The sealing bracket has a V-shaped cross-section, open at the inlet flow side of the medium to be filtered, so that the sealing bracket, under elastic pretension, lies sealingly against the housing. This solution produces good results, but requires additional space at the side. Additional space, during the filtering procedure, is limited. In addition, under certain edge conditions, it turned out that mounting a radical-shape designed sealing and stiffening bracket was a problem.
The object of the present invention is to create a filter cartridge which is simple in its construction, and which can be inserted into a corresponding frame or housing without difficulty. The filter cartridge should also have the ability to form a good seal at its end faces running parallel to the folds.
In accordance with this object, a filter cartridge built according to the principles of the present invention has an accordion fold pack. The accordion fold pack is provided with closing elements. The closing elements include stiffening strips partially overlapping the accordion fold pack and sealing elements which are integrally connected to the stiffening strips. The stiffening strips are positioned at the end faces of the accordion fold pack, which run parallel to the folds.
During continuous production of accordion fold packs folded in a zigzag shape, the accordion fold packs are cut off to desired lengths. This produces a need to stiffen the end faces of the accordion fold packs and provide them with a sealing element. In order to arrive at the simplified specific embodiment of the sealing element, the stiffening strips are attached at the discharge side of the accordion fold pack. The attachment can be made, for example, using an adhesive or heat sealing procedure, depending upon which kind of material is planned for the closing elements.
In order to influence the flow-through of the filter cartridge as little as possible by the mounting of the stiffening strips at the edge region of the accordion fold pack, the stiffening strips can be developed in a saw tooth manner. It is also possible to use stiffening strips which are hole punched or perforated.
Mounting the stiffening strips on the discharge side of the accordion fold pack allows the sealing elements to be made of sealing flaps directed toward the intake side of the accordion fold pack. The filter cartridge is dimensioned so that the sealing flaps, with their areas adjoining the stiffening strips, fit into an insert opening of a frame or housing, as the case may be, while their areas lying farther out project beyond the insert opening, and are fitted into the opening with a slight press. Their end edges then lie sealingly against the housing wall. Preferably, the height of the sealing flaps is less than the height of filter folds, so that their outer edge can lie sealingly against the housing wall, which, as a general rule, has the same height as that of the folds. On the other hand, the sealing flaps should be dimensioned so that their height is at least 10% of that of the folds, so as to be able to cover a sufficient tolerance between the filter cartridge and the housing.
Depending on the available frame and the material used for the sealing elements, the sealing flaps can be bent convex or concave in their longitudinal direction. This allows higher pressure differences at the filter cartridge and the use of soft materials for the sealing elements. The existing pressure difference can then reinforce the sealing effect.
The sealing elements can also take the form of a hose in an exemplary embodiment. In the simplest solution, the sealing flap, rolled into a hose, can be joined at its outer edge to the stiffening strip. However, for technical production reasons, the sealing elements preferably are made of a slitted, hose-like roll, having a stiffening strip joined at each slit edge. When combining this with the accordion fold pack, the two stiffening strips can then be connected to each other.
In another exemplary embodiment the sealing elements are U-shaped, with their free edges joined to stiffening strips. The stiffening strips are positioned both at the intake side and at the discharge side of the accordion filter pack. This embodiment also allows the flow direction to be changed.
In one embodiment, the stiffening strips and the sealing elements are made of a material of the same strength. They are connected to each other via a connecting fold. The stiffness of the material is chosen so that the filter cartridge is held in the housing or frame in a force locking way. The bending fold permits a minor degree of bending of the sealing element with respect to the stiffening strips.
It is also possible to design a closing element so that the stiffening strips and the sealing elements have a different strength and/or material density. This permits the filter to be adapted to a wide range of predefined conditions. It is also possible to form the stiffening strips and the sealing elements of different materials. Since the accordion fold packs are predominantly made of nonwoven fabrics, a nonwoven fabric is an obvious example material for the closing element. This allows the possibility of representing the filter as being made of uniform components. It is also possible to use thermoplastics as a working material.